Cod fish otoliths: information storage structures. In: The propagation of cod Gadus morhua L.: an international symposium, Arendal, 14 - 17 June 1983

The otoliths of cod fish may have incorporated within their structural and chemical components a large amount of lifehistory information. This information may be revealed when appropriate analytical methods are utilized. External and internal examinations of all three otoliths (sagitta, asteriscus and lapillus) for otolith macrostructure and microstructure by light and Scanning Electron Microscopy indicate that yearly, daily and population rhythmic patterns exist. These data make it possible to estimate the age of adult, juvenile and larval cod fish. Chemical analyses of otolith carbonate by mass spectrometer for stable isotopic concentrations and by atomic absorption and electron microprobe for strontium and calcium concentrations provide valuable insights into the past history of an individual fish. Stable isotopic concentrations of 18o and 16o appear to be directly related to temperature, and stable isotopic concentrations of 13c and 12c appear to mirror the nutritional and metabolic history of a fish. Strontium-calcium concentration ratios seem to be inversely related to temperature and electron microbe analyses make it feasible to interpret almost daily changes in temperature. A combination of structural and chemical analyses would make it possible to link growth and mortality rates to nutritional and environmental occurrences